Method for forming semiconductor structure

A method for forming a semiconductor structure, comprising:

• forming a first dielectric layer over a first metal layer, wherein a material of the first conductive layer is selected from the group consisting of W, Al and AlCu;
• exposing the first metal layer through a bottom of a trench in the first dielectric layer;
• forming a second metal layer in the trench and covering a top surface of the first dielectric layer, wherein a material of the second metal layer is selected from the group consisting of Ta, TiN, WN, W, Pd, NiCr, Zr, and Nb;
• removing a portion of the second metal layer such that a top surface of the second metal layer is lower than the top surface of the first dielectric layer;
• forming a third metal layer in the trench and covering the first dielectric layer, wherein a material of the third conductive layer is selected from the group consisting of TiN, TaN, and TaAlN;
• forming a second dielectric layer over the third metal layer and the first dielectric layer;
• removing a portion of the third metal layer and a portion of the second dielectric layer to expose the top surface of the first dielectric layer;
• and
• forming a phase change material over the first dielectric layer, the second dielectric layer and the third metal layer,
• wherein a top surface of the third metal layer is entirely in contact with the phase change material.

A method for forming a semiconductor structure, comprising:

• forming a first dielectric layer over a lower conductive layer, the first dielectric layer comprising at least one trench exposing the lower conductive layer, wherein a bottom surface of the first dielectric layer is aligned with a top surface of the lower conductive layer, wherein a material of the lower conductive layer is selected from the group consisting of tungsten (W), aluminum (Al), and aluminum copper (AlCu);
• forming a heat-buffering layer in the trench, wherein a material of the heat-buffering layer is selected from the group consisting of tantalum (Ta), titanium nitride (TiN), tungsten nitride (WN), tungsten (W), palladium (Pd), nickel chromium (NiCr), zirconium (Zr), and niobium (Nb);
• stacking a heat-spreading layer over the heat-buffering layer in the trench;
• filling the trench with a second dielectric layer;
• disposing a phase change material over the first dielectric layer;
• and
• forming a top electrode over the phase change material,
• wherein the second dielectric layer, the heat-spreading layer, and the heat-buffering layer form a bottom electrode, and a resistivity of the heat-buffering layer is less than a resistivity of the heat-spreading layer.